Slow reboots due to ZFS cleanup in kern_shutdown() .. zio_fini()

[Peter Eriksson]

zio_fini: kmem_cache_destroy(zio_buf_cache & zio_data_buf_cache):

zone_free_item(zone=UMA Zones): zone->uz_dtor() took 16 seconds
uma_zdestroy(zio_buf_12288) took 16 seconds
kmem_cache_destroy: uma_zdestroy(0xfffff8034678e980) [zio_buf_12288] took 16 seconds
kmem_cache_destroy(zio_buf_cache[20]) took 16 seconds

zone_free_item(zone=UMA Zones): zone->uz_dtor() took 60 seconds
uma_zdestroy(zio_buf_16384) took 60 seconds
kmem_cache_destroy: uma_zdestroy(0xfffff8034678e880) [zio_buf_16384] took 60 seconds
kmem_cache_destroy(zio_buf_cache[28]) took 60 seconds


Looks like it is the call to zone->uz_dtor that is taking time (added time check around the various parts of zone_free_item().

- Peter

> Indeed, looking at the vmstat -z output this doesn't really make sense.
> It would be useful to confirm that we are in fact spending most of the
> time reclaiming items.